Ion traps typically analyze ions using resonant ejection, as described in greater detail in U.S. Pat. No. 4,540,884, which is hereby incorporated by reference. Mass selective ejection can also be performed using linear ion traps, as described in U.S. Pat. No. 6,177,668, which is hereby incorporated by reference.
Both linear (2D) and three dimensional (3D) ion traps are commonly used for mass/charge measurement as stand-alone mass spectrometers, or as non-mass selective devices providing ion focusing for another mass measurement device. The use of ion traps to perform focusing prior to another mass analyzer is described in US Patent Application Publication No. 2005/0151073 A1 and PCT Application No. WO2005083742 A2. Ion traps have also been used in conjunction with orthogonal Time of Flight (o-TOF) analyzers allowing improvement in transfer efficiency and duty cycle. The development and characterization of ion traps as ion focusing devices is important not only for ion trap mass spectrometry but also to enable them to be coupled with other mass analyzing techniques for enhancing the overall performance of the mass spectrometer.
One common mass spectrometer is the Fourier Transform Ion Cyclotron Resonance (FTICR) Mass spectrometer. The FTICR consists of Fourier Transform analysis of ion trajectories in an ion trap and is the most expensive currently existing mass spectrometry technique. A single instrument typically costs over a million dollars. FTICR has been described by many people including: L. Chen, A. Marshall, Effect of Time-domain Dynamic Range on Stored Waveform Excitation for Fourier Transform Ion Cyclotron Resonance Mass Spectrometry, Rapid Commun. in Mass Spectrom. Vol, No. 3 1987, 39-42, which is hereby incorporated by reference.
An FTICR uses a Penning ion trap as described in F. M. Penning, Physica (Utrecht) 3, 873 (1936), which is hereby incorporated by reference. An explanation of ion confinement in a Penning ion trap is in P. K. Ghosh, Ion Traps, Oxford University Press, 1995, which is hereby incorporated by reference. Furthermore, different Pennning ion traps exist such as those described in G. Ciaramicoli, I. Marzoli, and P. Tombesi, Scalable Quantum Processor with Trapped Electrons, Phys. Rev. Lett. 91, 017901-1 (2003), which is also incorporated by reference.
Many attempts have been made to reduce the cost of this technique and apply it to ion traps which do not require superconducting magnets (as required by the FTICR). To date only one example gives high resolution mass spectra and was patented by A. Makorov (WO9630930, Applicant: HD Technologies limited (GB); (GB), Pub. Date 1996-10-03) which is hereby incorporated by reference. This allowed an instrument called an Orbitrap to be commercialized and an individual instrument costs several hundred thousand dollars. Despite the high price the Orbitrap is still very cheap compared to the FTICR and has sold widely since it was commercialized.
Other recent attempts to perform image current detection (FT analysis) in a 3D ion trap are described in Y. Zerega (Int. Conf. Mass Spectrom. Prague, Czech Republic, 2006) and G. Cooks (E. R. Badman, G. E. Patterson, J. M. Wells, R. E. Santini, R. G. Cooks, Differential non-destructive image current detection in a Fourier transform quadrupole ion trap. Journal of Mass Spectrometry, 1999, 34(8), 889-894), which are hereby incorporated by reference.
Several recent patents have also been filed by international mass spectrometry companies such as “Method and apparatus for Fourier Transform Mass Spectrometry (FTMS) in a linear multipole ion trap” was described by U.S. Pat. No. 6,784,421 B2 filed on 14 Jun. 2001 by M. A. Park patentability as well as GB 2418528 A with a priority data date of Jul. 2, 2004 and was filed on the Jul. 21, 2005 attributed to M. Green, R. H. Bateman and J. Brown describing “Detecting the frequency of ions oscillating along the longitudinal axis of a linear ion guide or trap” by Micromass.
Older attempts to perform FT-ion trap were made by the international company Thermo Finnigan and include the conference presentation: M. W. Senko, J. C. Schwartz, A. E. Schoen, J. E. P. Syka (48th ASMS conference on Mass Spectrometry and Allied Topics, Longbeach, Calif., 2000) and the U.S. Pat. No. 6,403,955 B1 (attributed to M. Senko and filed on 26 Apr. 2000).
S. Ring, H. B. Pederson, O. Heber, M. L. Rappaport, P. D. Witte, K. G. Bhusan, N. Alstein, Y. Rudich, I. Sagi, D. Zajfan, Anal. Chem. 2000, 72, 4041-4046 described image current detection in an electrostatic ion trap.
Although 3D ion traps can focus ion cloud sizes up to approximately 1 mm in diameter, their drawbacks include limitations in ion ejection and use as intermediate devices. Other mass spectrometry devices may include cons such as large size, limited applications, cost-effectiveness, a very large K.E. distribution of the ions on ejection, or other problems (e.g., the desired spatial dispersion, mass/charge measurement precision associated with radial and axial ion detection, electrode fabrication limitations, etc.). An example of the K.E. range that would be produced for a 3D ion trap is described in C. Marinach, A. Brunot, C. Beaugrand, G. Bolbach, J.-C. Tabet, Int. J. Mass Spectrom. 2002; 213:45, which is hereby incorporated by reference.
Accordingly, it is desirable to have an improved linear ion trap that is quick, space-efficient, affordable, and versatile for use with other mass spectrometry applications.